[libcxx-commits] [libcxx] [libcxx] Implementation of P1831R1 (PR #101439)

[A. Jiang via libcxx-commits]

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@@ -74,7 +74,7 @@ struct atomic<_Tp*> : public __atomic_base<_Tp*> {
   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR atomic(_Tp* __d) _NOEXCEPT : __base(__d) {}
 
   _LIBCPP_HIDE_FROM_ABI _Tp* operator=(_Tp* __d) volatile _NOEXCEPT
-    requires __base::is_always_lock_free
+    _LIBCPP_REQUIRE_IS_ALWAYS_LOCK_FREE
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frederick-vs-ja wrote:

> since virtually all systems with atomic instructions will support atomic reads and writes of pointer width

This is not guaranteed/required by the standard.

I think the approach in microsoft/STL#634 works - define a conditionally deprecated but always `true` constant and then `static_assert` it. With this approach you don't need to be worried about whether some atomic types are always lock-free.

https://github.com/llvm/llvm-project/pull/101439